1. Field of the Invention
The present invention relates to an internal combustion engine ignition apparatus mounted in, for example, an automobile, and particularly to an internal combustion engine ignition apparatus in which a current of a primary coil of an ignition coil is interrupted by a switching element, so that a high voltage for ignition is generated in a secondary coil of the ignition coil.
2. Description of the Related Art
In a conventional internal combustion engine ignition apparatus, as a switching circuit for opening and closing a switching element connected to a primary coil of an ignition coil, one having a power supply terminal connected to a battery, an output terminal connected to the primary coil of the ignition coil, an input terminal to which an ignition signal voltage is supplied, and a reference potential terminal is often used. In the internal combustion engine ignition apparatus having the four terminals of the power supply terminal, the output terminal, the input terminal and the reference potential terminal, an ignition control circuit is connected between the power supply terminal and the reference potential terminal, so that a stable voltage from the battery is applied to the ignition control circuit through the power supply terminal, and the ignition control circuit can be stably operated. However, since the four terminals including the power supply terminal is included, the terminal structure becomes complicated.
A conventional internal combustion engine ignition apparatus in which a terminal structure is simplified is disclosed in, for example, Japanese Patent No. 2,749,714. This internal combustion engine ignition apparatus does not have a power supply terminal connected to a battery, but is constructed by three terminals, that is, an output terminal connected to a primary coil of an ignition coil, an input terminal to which an ignition signal voltage is supplied, and a reference potential terminal, and its terminal structure can be simplified.
However, in the internal combustion engine ignition apparatus of this type which has no power supply terminal connected to a battery, since a switching element connected to the primary coil of the ignition coil is directly driven by the ignition signal voltage supplied to the input terminal, there is a disadvantage that variation in the reference potential level of the ignition signal voltage disturbs the timings when the switching element is turned on and off and degrades the ignition characteristic.
The ignition signal voltage is generated by, for example, an electronic circuit for controlling an internal combustion engine, called ECU, or the like. The ignition signal voltage is supplied to the input terminal of a switching circuit of the ignition apparatus. Here, consideration will be paid to a case where the reference potential terminal of the ECU is connected to a common potential point through a first parasitic resistor, and the reference potential terminal of the ignition apparatus is connected to the common potential point through a second parasitic resistor. In this case, the ECU is used for not only generation of the ignition signal voltage but also other signal processing, and in the case where the ignition signal voltage is generated in a state where a current flows through the first parasitic resistor, the ignition signal voltage is supplied to the input terminal of the ignition apparatus in the form in which a base voltage generated at both ends of the first parasitic resistor is added to the ignition signal voltage.
Since the level of the base voltage included in the ignition signal voltage is varied depending on the current of the ECU or the like, a level variation corresponding to the base voltage is eventually given to the ignition signal voltage. The ignition apparatus brings the switching element into an on state at, for example, an energization timing when the level becomes a predetermined value or higher in a rising portion of the ignition signal voltage, and brings the switching element into an off state at an ignition timing when the level becomes the predetermined value or lower in a falling portion of the ignition signal voltage. However, the variation in the base voltage included in the ignition signal voltage disturbs these timings and degrades the ignition characteristic of the ignition apparatus.
The variation in the energization timing varies, for example, an energization time of the primary coil of the ignition coil, and varies ignition energy. Besides, the variation in the ignition timing varies an ignition timing to an engine, and lowers the output of the internal combustion engine. At the worst, due to a rise in the level of the ignition signal voltage, it becomes impossible to turn off the switching element in the falling portion of the ignition signal voltage, and misfire is caused.